1. Field of the Invention
The present invention relates to a driving method of a liquid crystal display device, more specifically, an improved driving method for a simple matrix type liquid crystal display device. Moreover, the present invention relates to a liquid crystal display device which uses the above driving method for a liquid crystal display device. Furthermore, the present invention relates to electronic equipment comprising such a liquid crystal display device. In addition, the present invention relates to a driving circuit which drives such a liquid crystal display device.
2. Description of Related Art
A driving method for a conventional simple matrix type liquid crystal display device method selects the scanning electrode(s) in order, one by one.
Another driving method for a conventional simple matrix type liquid crystal display device is a driving method commonly known as the IHAT driving method, wherein a plurality of scanning electrodes are simultaneously selected using an orthogonal matrix while maintaining their orthogonality. This driving method is disclosed in a Generalized Addressing Technique for RMS Responding Matrix LCDS, 1988 International Display Research Conference P80-P85, in which the article states that the lowering of voltage for a liquid crystal display device is feasible.
However, although conventional simple matrix type liquid crystal display devices are advantageous in the sense that manufacturing costs are less expensive than for an active matrix type liquid crystal display, they are disadvantageous in another sense that both high speed response characteristics and excellent contrast characteristics are not satisfied.
A technology commonly known as the multi-line driving method is disclosed in U.S. Pat. No. 5,262,881, and in the international patent application WO93/18501 wherein such problems of conventional simple matrix type liquid crystal display device are resolved and both high speed response characteristics and excellent contrast characteristics are satisfied by dividing the selection period into a plurality of sub-selection periods, the sub-selection periods being scattered within one frame period.
The multi-line driving methods disclosed in the above public notices are described hereafter with reference to FIGS. 20 through 23.
To begin with, the liquid crystal display device for which the multi-line driving methods are applied is a simple matrix type liquid crystal display device (200) and comprises a plurality of scanning electrodes (203), a plurality of signal electrodes (204), and display elements (Eij). Moreover, scanning signals (X1-Xn) are applied to the scanning electrodes to provide selection signals (V1 or -V1) for selection periods and non-selection signal (0V) for non-selection periods while data signals (Y1-Ym) are applied to the signal electrodes based on the display data. The display element is driven by the scanning signals and data signals.
The scanning electrodes are divided into a plurality of groups, and selection signals (X1-X4) which are mutually orthogonal in one frame are given in bulk for each of the scanning electrodes belonging to the same group.
The selection period is divided into four mutually exclusive sub-selection periods (t11-t41) with the selection signal electric potential being established for each of four sub-selection periods.
The data signals (Y1, Y2, . . . ) are determined by comparing the polarity (+/-) of the electric potential of the selection signals based on the electric potential of the non-selection signals and the display data of the display elements.
However, with such a driving method, there has been a problem of uneven display in the direction of signal electrodes (normally the vertical direction). In explaining the reason for the problem with reference to FIG. 21, the cause of the problem is that when the data signal with the pattern described by Y1, (for example, the data signal to which voltage V3 is applied only for the period described by 2f in one frame and no voltage is applied for other periods), is applied to the signal electrodes, a shift based on time occurs in the distribution of the voltage applied to the display elements (Eij) compared to other patterns displaying the same luminance signals, causing an uneven display. This uneven display is especially noticeable when the response is fast.
Moreover, such a driving method presents another problem in which the unevenness of the display becomes severe and flickering occurs when the display contents are changed one after another. This problem is explained with reference to FIG. 22. The driving method of FIG. 22 is similar to the driving method used in FIG. 21. In the first selection period t11, selection signals comprising scanning signals X1-X4 are simultaneously applied to the first four scanning electrodes and in the next selection period t12 (not shown), selection signals comprising scanning signals X5-X8 (not shown) are applied simultaneously to the next four scanning electrodes. This voltage application is repeated for all of the scanning electrodes (X1-Xn) and for all of the field (1f-4f). Luminance (transmittance rate or reflection rate) (T1, T2) changes one after another based on the voltage applied to the display elements.
If the display screen does not change between the first frame and the second frame, then the change in luminance is periodic (see T1) and the unevenness of the display does not become especially severe. On the other hand, if the display screen changes between the first frame and the second frame, then the change in the luminance is not periodic (see T2) and the unevenness of the display becomes especially severe and flickering occurs.
As explained above, the driving method disclosed in the U.S. Pat. No. 5,262,881 and the driving method disclosed in international application WO93/18501 have the merit of improving the problems of poor response characteristics and extremely low contrast characteristics in a conventional simple matrix type liquid crystal display device. However, these driving methods have their own problems such as (1) an uneven display occurs in the direction of the signal electrode (normally the vertical direction) and (2) the uneven display becomes especially severe and flickering occurs when the display contents change one after another.
The present invention aims to resolve the problems of the above-stated conventional driving methods by providing a driving method of the liquid crystal display device capable of (1) controlling the unevenness of display in the direction of signal electrode(s) (normally the vertical direction) and (2) not causing an especially severe uneven display in the direction of the signal electrode(s) nor flickering even when the display contents change one after another.